The present invention relates to a terminal connector for high-energy electric cables with internal cooling, particularly for water-cooled cables.
There are already known various terminal connectors for, on the one hand, supplying the electric current and the cooling medium, such as oil or water, to the cable and, on the other hand, for withdrawing the electric current and discharging the spent cooling medium from the cable at a distance. The known terminal connectors usually comprise two distinct terminal connector assemblies, one for the electric current and the other for the cooling medium. When considered in the direction of flow of the cooling medium, the terminal connector assembly for the cooling medium is upstream of the terminal connector assembly for the electric current at the upstream end of the cable, and downstream thereof at the downstream end of the cable. A connecting pipe connects the two terminal connector assemblies at each end of the cable and conducts the cooling medium from one of the assemblies to the other.
In the conventional terminal connectors of this type, the high electric potential of the cooling medium is caused to decline in the cooling medium terminal connector assembly. Throughout the specification, the present invention will be discussed as embodied in a water-cooled high-energy cable, but the concept of the invention can be equally advantageously utilized in any cable with internal cooling with employs a cooling other than water. When the water is used as the cooling medium, it is already known to construct the water terminal connector assembly as a substantially tubular insulator which is, on the one hand, so constructed as to be capable of withstanding the flow of the cooling water therethrough and, on the other hand, is capable of preventing an electric discharge over its outer surface even when the latter is contaminated.
The conventional terminal connectors of this type are provided with channels which, in order to obtain advantageous flow conditions therein, have exactly the same dimensions as the cooling channel provided in the electric cable and serving the purpose of cooling the electric conductor of the cable. However, the experience has shown that such a selection of the dimensions of the cooling channel of the terminal connector is less than advantageous. One particular disadvantage of such conventional terminal connectors is that, in order to keep the electric current flowing through the water in the region of the terminal connector, and the elevation of the temperature of the cooling water in such a region caused by the flow of the electric current therethrough, to a minimum, it is necessary to use as the cooling medium water of a high degree of purity, since such a highly pure water possesses a high specific resistivity coefficient, so that the amount of the electric current passing through the water in the region of the terminal connector is kept relatively low. It is true that it is possible to fill the cable with highly purified, decontaminated and de-ionized water; however, during the operation of the cooling system for cooling the cable, it is impossible to assure that some contaminants will not be entrained in the cooling water, such as, for instance, particles and impurities resulting from erosion of the inner surface of the cooling channel of the cable. Of course, the entrainment of the impurities results in an increase of the conductivity of the cooling water which, in turn, results in an increase in the current flowing through the water in the region of the terminal connector. These undesirable contaminants can be removed from the water, for example, by continuous purification of the cooling water during the operation of the cable and of the cooling system, or by replacing the contaminated cooling water after a certain period of operation of the cooling system by a new, purified cooling water. However, both of the above-described methods of keeping the cooling water devoid of contaminants are relatively expensive and increase the overall cost connected with construction and operation of the cable.